Attic Ventilation Ratio

1 square foot of net free vent area nfva per 150 feet of attic floor.

Attic ventilation ratio. Allows cool dry air to enter the attic. There should also be a 50 50 balance of attic venting and roof venting. 1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below. The recommended ventilation ratio to provide for vented attic assemblies when an air barrier is present is the 1 300 ratio as specified by most building codes.

Remember the minimum area requirement when using a continuous system is a ratio of 1 300. You can also contact your local municipality to check on building code in your area. Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation. That said air resistance and interference such as vent grates reduces the area of true ventilation.

Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. Without exception you should talk to a professional to determine what your home requires. Ventsure inflow intake vent. Always have a balanced ventilation system.

If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation. Building codes vary. Now let s figure out how much ventilation space we need. Ok so now we know the square footage of the attic area to be ventilated.

The following product options will allow you to achieve an intake nfva of 528 square inches. This is based principally on good historical experience and simple psychrometric analysis handegord giroux 1984. Most building codes require a ratio of 1 150 ventilation space to attic floor space. So in our example we will divide the 1 500 square feet by 300.

Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space. Of vent for every 300 sq. Choose one of the following products to meet the recommended intake nfva of 528 square inches. 1 300 ventilation ratio recommended.